A model of resource use, using data from 33 institutions for mental diseases, was tested. The model posits average cost per patient as a function of facility size, average occupancy, hourly wages for staff, client age distribution, client gender, length of stay, client history with criminal justice system, level of client confusion, suicidal tendencies among clients & threatening behaviour among clinets. The model is suggested as a possible basis for a payment system. (30 refs.)